Engine-starting systems

ABSTRACT

In an engine-starting system there is a starter circuit for starting the engine in the usual way, but in the starting circuit is provided means for breaking the transistor circuit when the engine speed is above a predetermined value. Conveniently this means is a transistor in series with a relay controlling the starter, and this transistor is turned off when the engine speed is above a predetermined value. However, delay means is provided for keeping the starter circuit broken for a predetermined period of time after the engine speed falls below the predetermined value.

United States Patent [721 In n David Wilsy 2,020,750 11/1935 Wertz 29037 4A s Street, Wflull, Sawmill"; 2,035,820 3/1936 Maurer 290/38 MaurJames Allnortflo Stew RM, 2,165,133 7/1939 Cuthbertson.... 290/38 lWorcester, l 3,167,659 1/1965 Cromwell 290/38 1 1 p 28,314 3,440,4334/1969 Coman 290/38 1 Filed Apr-14,1970 3,443,112 5/1969 Huntzinger...290138 1 1 Patented 099-11, 1971 3,452,210 6/1969 Gray et al. 290/38[32] Priority May 12, 1969 [331 GR Britain Primary Exammer-G. R. Slmmons[31] 24,054l69 Attorney-Holman, Glascock, Downing & Seebold [54]ENGINBSTARTING SYSTEMS AIQSTRACT In an engine-starting system there is astarter eir- 2 Chin, 1 Drum. m cu1t for starting the engine in the usualway, but 1n the starting circuit is provided means for breaking thetransistor circuit [52] US. Cl 290137, when the engine spud is abovc apredetermined vahm 290,38 veniently this means is a transistor in serieswith a relay con [51] B Cl 11/00 trolling the starter, and thistransistor is turned off when the [50] Field of Search 290/36, 37,engine Spud is above a predetermined value However, delay 38; 123/179means is provided for keeping the starter circuit broken for aReferences Cited predetermined period of time after the engine speedfalls UNITED STAT S PATENTS below the predetermmed value.

1,979,302 11/121115 Whitney 290/37 X ENGINE-STARTING svsrssrs Thisinvention relates to engine-starting systems, particularly, although notexclusively, for diesel-engined vehicles.

A system according to the invention comprises a starter circuit forstarting an engine, means for breaking the starter circuit when theengine speed is above a predetermined value, and delay means operablewhen the engine speed falls below said predetermined value for keepingthe starter circuit broken for a predetermined period of time.

The invention is designed to minimize the possibility of damaging thestarter by trying to start the engine when it is running. Thus, thestarter circuit is automatically cutout at a predetermined engine speed,so that a second attempt cannot be made to start an engine once it hasalready started. There is still a danger that an attempt can be made tostart an engine when the speed of the engine is falling but the enginehas not stopped, and the delay means is incorporated to prevent thispossibility.

An example of the invention is illustrated in the accompanying circuitdiagram.

Referring to the drawings, the vehicle with which the system isassociated has a battery 5 with positive and negative terminals 11, 12the battery being charged through a full-wave rectifier 7 by analternator 6 driven by the engine. The output from the alternator isalso fed through three further diodes 8 to a terminal 9 which isconnected to a voltage regulator (not shown) controlling the alternatoroutput by varying the current flow in its field winding. The terminals9, 11 are interconnected through a warning lamp 30 in series with aswitch 25 which will, on a diesel engine vehicle, be the auxiliaryswitch of the vehicle, but in a spark ignition system will be theignition switch. The alternator also has one phase point connected to aterminal 10 at which an AC output is obtained at a frequency dependenton the speed of rotation of the alternator, which in turn is dependenton engine speed.

The terminal 11 is connected through the switch 25, a starter switch 13and a winding 14 in series to the collector of an NPN transistor 15 theemitter of which is connected to the terminal 12. The winding 14 isbridged by a diode 16, and the junction of the winding 14 and switch 13is connected through a normally open pair of contacts 17 and the startersolenoid 18 in series to the terminal 12. The contacts 17 are closed bythe winding 14 when the winding 14 is energized.

The collector and base of the transistor 15 are bridged by a diode 19,and the base of the transistor is connected through a Zener diode 21 tothe collector of an NPN transistor 22 having its emitter connectedthrough a resistor 23 to the line 12. The collector of the transistor 22is connected through a resistor 24 to junction of the lamp and switch25, and the emitter of the transistor 22 is connected through a resistor26 to the same junction.

The circuit further includes a resistor 27 and a diode 28 connected inseries between the collector of the transistor 15 and the base of thetransistor 22 to provide a feedback path. Moreover, the base of thetransistor 22 is connected to the terminal 10 through a diode pumpcircuit which includes a capacitor 29 and a diode 31 in series betweenthe terminal 10 and the base of the transistor 22, together with a diode32 connecting the junction of the capacitor 29 and diode 31 to theterminal 12, and a capacitor 33 and a variable resistor 34 in parallelbetween the base of the transistor 22 and the terminal 12.

The terminal 10 is further connected to the terminal 12 through a diode35 and a capacitor 36 in series, the junction of the diode 35 andcapacitor 36 being connected through a variable resistor 37 and a diode38 to the collector of the transistor 15.

When it is desired to start the engine, the switch 25 must developedacross the Zener diode 21 to render it conductive,

so that current flows through the resistor 24 and Zener diode to turn onthe transistor 15. At this s ta e there is no base current supplied tothe transistor 22, WhICr is therefore oft. When the switch 13 is closed,current flows through the winding 14 and the transistor 15 so that thecontacts 17 close and the solenoid 18 is energized. The alternatorimmediately produces an output, and thereafter the lamp 30 isextinguished and the supply to the terminal 9 is by way of the diodes 8.As soon as the alternator produces an output, the diode pump circuitacts in known manner to produce across the resistor 34 a voltage whichrises with engine speed. The emitter voltage of the transistor 22 is setby the resistors 26 and 23 and as the base voltage rises a condition isreached, at a predetermined engine speed, at which the transistor 22starts to conduct so that current flowing through the resistor 24 isdiverted through the transistor 22. As the transistor 15 starts to turnoff, the current flowing through the diode 38 and the transistor 15 isdiverted through the base emitter of the transistor 22 to assist turn onof the transistor 22, this feedback increasing the switching speed ofthe circuit. The Zener diode 21 enables the transistor 15 to be turnedoff even though the emitter of transistor 22 is at a higher voltage thanthat required to turn on the transistor 15. Thus, the circuit switchesrapidly to a condition in which the transistor 22 is on and thetransistor 15 is off, so that the winding 14 is deenergized and thecontacts 17 open to break the starter circuit. The starter circuitremains broken as long as the engine speed is above the predeterminedvalue. How ever, when the engine speed falls below the predeterminedvalue, the voltage produced across the resistor 34 by the diode pumpcircuit will fall below the level at which the transistor 22 conducts,and so the circuit would be capable of reverting to its condition withthe transistor 15 on and the transistor 22 off. The return to thiscondition is, however, delayed by the delay network. This delay networkincludes the capacitor 36 which charges by way of the diode 35, and thendischarges through the resistor 37 and diode 38, and thence through theresistor 27 and diode 28 to hold the transistor 22 on for apredetermined period of time which will be chosen so that the enginespeed will fall to zero.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. An engine-starting system for a road vehicle having a battery and analternator driven by the engine for charging said battery, said systemcomprising in combination a starter circuit for starting the engine, adiode pump circuit operated by said alternator for producing an outputdependent on engine speed, a switching circuit operated by the outputfrom said diode pump circuit for breaking the starter circuit when theengine speed is above a predetermined value, said switching circuitincorporating a first transistor which is turned on by the diode pumpcircuit at said predetermined engine speed, a second transistor in thestarter circuit which is turned off when the first transistor conducts,a Zener diode through which the base of said second transistor issupplied with current, and a feedback circuit between the first andsecond transistors for increasing the base drive to the first transistoras the second transistor starts to turn off, said system furtherincluding delay means operable when the engine speed falls below saidpredetermined value for keeping the starter circuit broken for apredetermined period of time.

2. A system as claimed in claim 1 in which the delay means includes acapacitor which is charged by the alternator phase output and holds thefirst transistor on for said predetermined period of time after theoutput of the diode pump circuit has fallen to a value at which thefirst transistor could have turned off.

1. An engine-starting system for a road vehicle having a battery and analternator driven by the engine for charging said battery, said systemcomprising in combInation a starter circuit for starting the engine, adiode pump circuit operated by said alternator for producing an outputdependent on engine speed, a switching circuit operated by the outputfrom said diode pump circuit for breaking the starter circuit when theengine speed is above a predetermined value, said switching circuitincorporating a first transistor which is turned on by the diode pumpcircuit at said predetermined engine speed, a second transistor in thestarter circuit which is turned off when the first transistor conducts,a Zener diode through which the base of said second transistor issupplied with current, and a feedback circuit between the first andsecond transistors for increasing the base drive to the first transistoras the second transistor starts to turn off, said system furtherincluding delay means operable when the engine speed falls below saidpredetermined value for keeping the starter circuit broken for apredetermined period of time.
 2. A system as claimed in claim 1 in whichthe delay means includes a capacitor which is charged by the alternatorphase output and holds the first transistor on for said predeterminedperiod of time after the output of the diode pump circuit has fallen toa value at which the first transistor could have turned off.